Liquid supply systems often include a pump that pumps liquid from a source to a destination system. In a residential water supply system, for example, a pump may be used to pump water from a source, such as a well or a water treatment system, to the home. In such systems, the water is often used irregularly in the home and a relatively small, pressurized cycle tank may be used to hold water before being supplied to the home. The pump generally operates in response to pressure to pump water to the home and/or cycle tank. For example, the pump may be switched on when the pressure drops to 50 PSI (i.e., when the cycle tank is drained) and may be switched off when the pressure rises to 70 PSI (i.e., when the cycle tank is filled). When the water is turned on in the home, for example, a sudden drop in pressure as the cycle tank drains causes the pump to be switched on and a sudden increase in pressure as the pump fills the cycle tank back up causes the pump to be switched off. With relatively small cycle tanks (e.g., 2.1 gallons), the pump will often be switched on and off multiple times during a single use due to the sudden pressure changes. The repeated switching may cause damage to the pump and the pump motor.
To provide constant pressure and avoid the “short cycling” of the pump when using relatively small cycle tanks, electronic automatic pump controls have been used. These controls generally include a pressure switch (e.g., set at 50 PSI on and 70 PSI off), a flow switch (e.g., set at 1 GPM), and a time delay (e.g., set at 8 seconds). When used with a 75 PSI maximum pressure pump, for example, the electronic pump control may be programmed to start the pump at 50 PSI and stop the pump 8 seconds after the pressure is over 70 PSI and the flow is less than 1 GPM. Electronic pump controls use pressure regulators where the pump pressure exceeds typical house pressures (e.g., 75 PSI). Due to their complexity, electronic pump controls are susceptible to leaks and electronic failures and may not be repairable or easily serviced. Other problems with electronic pump controls include an inconsistent turn-on pressure and low sensitive flow switch causing cycling even at higher flow rates (e.g., at shower flows of 2.5 GPM).
Mechanical pump controls are also available, such as the type disclosed in U.S. Pat. No. 5,988,984, which is incorporated herein by reference. These controls generally include a pressure switch, a pressure regulator, and 1 GPM bypass flow stream around the pressure regulator. When used with a 75 PSI maximum pressure pump, for example, the pressure regulator is generally set at 65 PSI and the pressure switch is set to start the pump at 50 PSI and stop the pump at 70 PSI once flow drops below 1 GPM, allowing the bypass flow stream to slowly build pressure to 70 PSI. One problem with this type of pump control is the loss of outlet pressure, which may be 10 PSI or more considering fall off pressure at higher flows. Such a loss of pressure is often undesirable, for example, in a residential system. Existing mechanical pump controls are also relatively expensive and also have many intricate parts resulting in a complexity that makes servicing such pump controls relatively difficult.
Short cycling may also be a problem in other liquid supply systems such as, for example, a residential fire sprinkler system. In such a system a pump may be used to pump water from a source, such as a water holding tank, to fire sprinkler heads. To avoid short cycling in these applications, a flow switch may be used to keep the pump running after a pressure switch starts the pump. Existing systems, however, often require extensive plumbing and wiring, are relatively complex, expensive and do not have a minimum run time delay.
Short cycling may also be a problem in various other liquid supply systems. In low flow residential whole house water treatment systems (e.g., reverse osmosis), for example, a pump may be used to pump water from a holding tank to a destination system in a home. In a low flow well water or city water supply for residential homes (e.g., with flows of 2.5 GPM or less), water may fill a holding tank and then may be pumped from the holding tank to the home. In a rainwater collection system, rainwater may fill a holding tank and then may be pumped from the holding tank to a destination system.
Other liquid supply systems in which short cycling may be a problem due to irregular water use include booster pump systems in which a pump may be used to boost town water pressure to one or more homes or commercial destinations and lawn or irrigation systems in which a pump may be used to pump from a source to drip irrigation and/or sprinkler heads.